A device to device proximity service (English full name: Device to Device Proximity Service, D2D ProSe for short) has become a research subject of the 3rd Generation Partnership Project (English full name: 3rd Generation Partnership Project, 3GPP for short) Long Term Evolution (English full name: Long Term Evolution, LTE for short) system Release 12 (English full name: Release 12, Rel. 12 for short). A physical layer of an LTE system provides a direct connection service for user equipments based on an orthogonal frequency division multiplexing-multiple-input multiple-output (Orthogonal Frequency Division Multiplexing-Multiple-Input Multiple-Output, OFDM-MIMO) technology. In this way, not only a service scope of the LTE system is expanded, but also D2D communication between user equipments can be used by more users.
In an LTE D2D ProSe service, in an application scenario, a UE-to-UE relay method is used. That is, one UE relays data of another UE, to increase a transmission distance.
In the LTE D2D system, when sending a D2D signal, UE needs to send scheduling signaling on a scheduling assignment (English full name: scheduling assignment, SA for short) resource, and then sends a corresponding D2D signal in a data resource pool. When a D2D terminal sends scheduling signaling on an SA resource, the scheduling signaling includes a destination address of a signal to be sent.
Referring to FIG. 1, FIG. 1 shows an LTE D2D system. An LTE base station and four UEs are included in the system. To send a D2D signal, UE1 needs to send scheduling signaling on a corresponding SA resource, and sends a corresponding data signal in a data resource pool matching the SA resource. The scheduling signaling sent by the UE1 on the SA resource includes a destination address of the data signal. Assuming that the UE1 needs to communicate with UE3, the destination address is an address of the UE3.
If UE2 is used as a relay to forward the D2D signal sent by the UE1, the UE2 needs to first receive data sent by the UE1, and then send the received data. Therefore, when relaying the signal sent by the UE1, the UE2 needs to receive the SA scheduling signaling sent by the UE1. In addition, when relaying the signal sent by the UE1, the UE2 also needs to first send the scheduling signaling on an SA resource, and then send, in a data resource pool matching the SA resource, the data signal that needs to be relayed.
When relaying the D2D signal sent by the UE1, the UE2 also needs to receive, on an SA resource, the SA scheduling signaling sent by the UE1. In the prior art, to relay data sent by the UE1, the UE2 needs to receive all SA scheduling signaling on the SA resource, receive D2D data indicated by all the SA scheduling signaling, and then relay the received data. In this case, the UE2 may relay data that does not need to be relayed, resulting in resource and energy waste. In an extreme case, this may cause abnormal D2D communication.